Pistachio Bloom Cast Model Development

Developed by Katherine Jarvis-Shean & David da Silva, reviewed by Theodore DeJong & Louise Ferguson, Department of Plant Sciences, University of California, Davis

The parameters used in this pistachio bloom model are from Küden, A.B., Kaska, N., Tanriver, E., Tekin, H. and Ak, B.E. 1995. Determining the chilling requirement and growing degree hours of some pistachio nut cultivars and regions. Acta Hort. 419:85-90.

Küden et al. calculated chilling requirement using Chill Units. Chill Unit calculations, following Richardson et al. (1974), assign an hour at an optimum temperature (between 2.6 and 9.1°C) as one chill unit, with temperatures above and below that optimum valued less. Particularly high temperatures are assigned negative values. See About Chilling Units and Hours for more details.

Küden et al. calculated heat accumulation using Growing Degree Hours. Growing Degree Hours, following Richardson et al. (1975), assign an hour above the threshold temperature of 4.5°C as that temperature minus 4.5°C, up to 25°C. For example, an hour at 9.5° would have a value of 5 Growing Degree Hours. All hours with temperatures above 25°C count for 20.5 GDH.

The model was developed using an Iranian cultivar, 'Ohadi'. However, it was found to estimate bloom in California cultivars: 'Kerman', 'Golden Hills', 'Lost Hills', 'Peters' and 'Randy' better than any other model in the literature.